A large new study conducted by Swedish researchers has found that older women who consumed more than 1,400 milligrams (mg) of calcium per day (from food and calcium supplements combined) were more than twice as likely to die from heart disease as those who consumed 600 mg to 1,000 mg of calcium per day.

Calcium is a nutrient that is known to be important for bone health. In fact, “Supplemental use of calcium has become common, and more than 60% of middle aged and older women in the United States are regular users of calcium supplements,” the researchers reported.

However, like three other recent studies cited by the researchers, the new study suggests that older women who take high doses of calcium may be significantly increasing their risk of cardiovascular disease and death.

In the new study, the Swedish researchers followed a group of 61,433 older women for an average period of 19 years. The study, “Long term calcium intake and rates of all cause and cardiovascular mortality: community based prospective longitudinal cohort study,” was published online February 13, 2013 in the British Medical Journal (BMJ).

Separately, a U.S. Government task force (the United States Preventive Services Task Force) reported on February 25, 2013, that taking low doses of calcium (less than 1,000 mg per day) and vitamin D (less than 400 iu per day) supplements could increase the likelihood of kidney stones, but “has no net benefit for the primary prevention of fractures” for post-menopausal women.

The Task Force formally recommended that healthy post-menopausal women should not take low daily doses of vitamin D and calcium to prevent bone fractures.

The Swedish Study; Method

In the new Swedish study, Dr. Karl Michaëlsson, Professor in the Department of Surgical Sciences, Section of Orthopedics at Uppsala University, Uppsala, Sweden, and colleagues, followed 61,433 older Swedish women (born between 1914 and 1948) for an average period of 19 years.

Based on questionnaires administered at the beginning of the study and again 10 years later, they assessed the women’s diet and calcium intake, as well as other health and lifestyle factors and educational level. Total daily calcium intake was measured as the estimated sum of calcium from the diet and from calcium supplements, combined.

For those participants who died during the study period, the researchers confirmed causes of death based on the official Swedish government cause-of-death registry administered by the Swedish National Board of Health and Welfare.

During a median average of 19 years of follow-up, 11,944 women (17% of the study participants) died. “Of these women, the underlying cause of death was cardiovascular disease in 3,862 [women], ischaemic heart disease in 1,932 [women], and stroke in 1,100,” of the women, the researchers reported.

The researchers performed statistical analyses to measure the association of high doses of daily calcium intake (higher than 1,400 mg per day) with rates of death from cardiovascular disease or stroke, compared to the association of low doses of daily calcium intake (600 mg to 1,000 mg per day) with death from those causes.

Findings

After controlling for other factors that could have predicted cardiovascular disease, including physical activity level, education, smoking, alcohol consumption and other dietary factors, the researchers found that the women who consumed 1,400 mg or more of calcium per day had more than twice the risk of death from heart disease, compared with the women who consumed between 600 and 1,000 mg of calcium per day.

The women who consumed 1,400 mg or more per day of calcium had a 114% higher risk of death from ischaemic heart disease, a 49% higher rate of death from cardiovascular disease, and a 40% higher risk of death from any cause, than the women who consumed lower doses of calcium (600 mg to 1,000 mg) per day, the researchers found. They did not find a significant correlation between level of calcium consumption and rate of death from stroke.

The study authors wrote, “The highest rates of death from all causes, cardiovascular disease, and ischaemic heart disease but not stroke were observed among those with a dietary calcium intake higher than 1400 mg/day. These intakes, compared with dietary intakes between 600 and 1000 mg/day, conferred hazard ratios of 1.40 (95% confidence interval 1.17 to 1.67) for all cause mortality, 1.49 (1.09 to 2.02) for cardiovascular disease mortality, and 2.14 (1.48 to 3.09) for ischaemic heart disease mortality.”

The study found the increased risks only for women who consumed the highest levels of calcium; the findings did not show any gradual increase in risk with gradually increased calcium consumption.

Conclusions; Implications of Study

“When looking at the totality of our data, high calcium intakes were associated with higher rates of death from all causes and cardiovascular disease. Mortality was not increased between 600 and 1400 mg/day of total calcium intake, the most customary levels of intake in this setting,” the authors concluded.

As to how high levels of calcium may act to increase risks of cardiovascular disease and death from cardiovascular causes, the authors noted that calcium can increase blood levels of “fibroblast growth factor 23,” a protein associated with higher risk for cardiovascular disease.

In detail, the authors explained:

“Calcium enriched meals can reduce calcitriol, the active vitamin D metabolite, by inhibition of 1α hydroxylase53 and also increase serum levels of fibroblast growth factor 23. Higher levels of circulating fibroblast growth factor 23 are associated with an increased risk of cardiovascular events and all cause mortality. In addition, fibroblast growth factor 23 downregulates calcitriol levels. Vitamin D suppression leads to an upregulation of the renin-angiotensin-aldosterone system and hypertension, higher levels of proinflammatory cytokines involved in the pathogenesis of atherosclerosis, increased carotid artery intima medial thickness, decreased edothelial function, hypertrophy of cardiac and vascular muscle cells, and a possible increase in serum triglycerides. Finally, high serum calcium levels can increase the risk of cardiovascular mortality by induction of a hypercoagulable state.”

“If you have a normal diet, you don’t need to take calcium supplements,” the lead author, Dr. Karl Michaëlsson, a professor and orthopedic surgeon at Uppsala University in Sweden told the New York Times. “Calcium supplements are useful if you have a very low intake of calcium, but few women have such a low intake,” Dr. Michaëlsson concluded.

Based on an extensive review of the relevant scientific literature and published studies, the Task Force concluded, “Lower doses of vitamin D and calcium supplements [400 IU or less of vitamin D3 and 1,000 mg or less of calcium] do not prevent fractures in older women and may increase the risk of kidney stones.”

The Task Force also concluded that: “(1) There is not enough evidence to determine whether vitamin D and calcium supplements can prevent fractures in men and in women who have not yet gone through menopause, [and] (2) There is not enough evidence to determine whether vitamin D and calcium supplements at larger doses can prevent fractures in older women.”

Following are the Task Force’s Final Recommendations on Calcium Supplementation to Prevent Fractures:

“The Task Force concludes that the current evidence is insufficient to assess the balance of benefits and harms of combined vitamin D and calcium supplementation for the primary prevention of fractures in premenopausal women or in men.

The Task Force concludes that the current evidence is insufficient to assess the balance of the benefits and harms of daily supplementation with greater than 400 IU of vitamin D3 and greater than 1,000 mg of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women.

The Task force recommends against daily supplementation with 400 IU or less of vitamin D3 and 1,000 mg or less of calcium for the primary prevention of fractures in noninstitutionalized postmenopausal women.”

The Task Force clarified that its findings and recommendations apply only “to adult men and women who live at home and not in assisted living or in nursing homes. It does not apply to people who have been diagnosed with osteoporosis or vitamin D deficiency.”

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